1. Field of the Disclosure
The subject disclosure relates to bearing enclosures with wear detection, and more particularly to an improved wear detection mechanism based on sensing a damaged ball cage.
2. Background of the Related Art
In aircraft and other applications, generator designs commonly use life lubricated deep groove ball bearings to support rotor loads. The bearings are also replaced at established intervals to avoid costly repairs and/or malfunctions. A typical DC air cooled generator often has auxiliary bearing systems to prevent potentially catastrophic failure. The auxiliary bearing supports the rotor load after the main bearing has failed.
Systems are designed such that a bearing failure sensor alerts the flight crew that wear has been detected in the main bearing. Under current guidelines, the airline may continue revenue flight operations for a limited number of hours from the alert, after which the generator must be removed for bearing replacement. One advantage of the auxiliary bearing system for the aircraft operator is to avoid dispatch delays caused by a generator bearing failure and the immediate need for aircraft maintenance.
There are problems associated with prior art bearing wear detection systems. Prior art systems rely on recognizing increase in radial play due to bearing wear. For preloaded bearings, determining the radial play is difficult and inexact, which often results in delay in bearing wear detection. Further, the prior art technology was acceptable for steel ball bearing designs since the steel balls progressively wear creating the radial play in advance of catastrophic ball cage damage. However, ceramic ball bearing designs wear differently, which prevents these methods from being optimal.
It is desirable to use ceramic balls in the main bearings because ceramic balls increase the life of the bearing. Although the ceramic balls are very robust, the other components may stop to function properly causing failure. A common failure mode of a ceramic deep groove ball bearing is that the grease degrades which causes the ball cage to fail from dynamic instability. Eventually parts of the ball cage are expelled from the bearing. It is noteworthy that because the bearing is preloaded, the ball cage failure does not result in a significant increase in radial play. Thus, cage damage may go undetected for some time. Frequently, as radial play increases, the gathered balls bind the inner ring and outer ring which normally causes the outer ring to rotate in the bearing liner bore. Continuous operation under these conditions causes damage to generator components and also imparts heat and high loading on the auxiliary bearing. As the bearing reaches the end of usefulness, radial play increases only after the cage has been consumed and considerable wear occurs on the inner and outer rings of the bearing. Examples of bearing wear detection systems are shown in U.S. Pat. No. 6,100,809 issued on Aug. 8, 2000 to Novoselsky et al. and U.S. Pat. No. 6,119,504 issued on Sep. 19, 2000 to Claus, each of which is incorporated herein by reference in its entirety.